Communication systems often balance transmitted signal quality against a risk of interference. The best possible signal quality is desirable because a high quality signal best insures that communicated information will be accurately received. Many factors influence signal quality at a receiver. These factors include transmission power level, transmitter and receiver antenna design and orientation, distance between transmitter and receiver, environmental conditions, background noise or interference, and the like. However, if all other factors are equal, a higher transmission power level usually leads to a better quality signal, and a communication system typically uses as high a transmission power level as possible to achieve good signal quality at a receiver.
Conversely, many communication systems simultaneously attempt to minimize the transmission power level. In battery operated systems, the minimization of transmission power conserves battery reserves. In addition, regulations and/or frequency reuse schemes dictate the use of lower power levels to prevent interference with other communications taking place far away from the transmitter and receiver over the same spectrum.
Thus, communication systems control power levels to accomplish the conflicting goals of good signal quality and no interference. To satisfy these conflicting goals, many communication systems need to keep transmission power levels just high enough so that an adequate signal quality is maintained at a receiver, but no higher. However, the factors which influence signal quality can change on a moment by moment basis. For example, movement between transmitter and receiver, rain, interference, and other factors may all quickly alter signal quality. Thus, many communication systems need to adjust transmission power levels on a moment by moment basis to compensate for the other factors that influence signal quality.
In conventional digital communication systems, a bit error rate (BER) parameter has been used to provide an indication of received signal quality. Thus, the BER parameter, if communicated to a transmitter, might potentially be useful in controlling transmission power levels. BER may be measured by communicating error detection and correction codes along with normal data and by keeping a count of the errors found through implementation of an error correction scheme. However, this measurement technique often requires the transmission of tens of thousands of symbols before reliable BER measurements are available. In communication systems where data are occasionally transmitted in bursts, a great length of time may transpire before a reliable BER measurement can be obtained. This great length of time makes the measurement technique too unresponsive for use in controlling transmission power on a moment by moment basis.
Other conventional communication systems estimate BER more quickly than it may be measured through monitoring error corrections. Conventionally, BER may be estimated by integrating a noise function over a constant period of time, frame, or number of symbols, or by integrating the noise function over a variable number of symbols and dividing an accumulated integration value by the number of symbols over which it has been integrated. The use of constant periods is a particularly undesirable solution when data are transmitted in bursts of varying length. In such situations, the constant integration period is limited to the worst case, shortest available period, and the shortest integration period yields the least accurate BER estimate. The technique of dividing an accumulated integration value by the number of symbols integrated is also undesirable. Division operations are typically complex operations which are implemented at great expense. In addition, the BER estimate so determined varies in accuracy.